The so-called ink jet or non-impact recording method is becoming popular as a method for converting image data in the form of electrical signals into hard copies because less noise is produced during recording than in impact recording. The ink jet method is also considered particularly useful because ordinary paper is usable without the need for a special process, such as fixing, for recording purposes.
An ink jet method that has already been put to practical use comprises the steps of filling an airtight container with ink, applying a pressure pulse thereto, and sending the ink out of the orifice of the container in a jet for recording purposes. Since the ink jet recorder for the aforesaid method cannot be made compact in view of its operating mechanism, the recorder requires scanning mechanically if recording has to be made with a desired image density. Consequently, the recording speed of this method has been unsatisfactory.
At the same time, there have been proposed techniques for remedying shortcomings inherent in the ink jet method and making high-speed recording possible. The magnetic ink jet method is a typical example of such improvement, which comprises arranging magnetic ink close to a magnetic electrode array, forming an ink-jet state corresponding in position to a picture element by making use of a swell of the ink in the presence of a magnetic field, and jetting out the magnetic ink in the static electric field. Since this method admits of electronic scanning, high-speed recording becomes possible but it is still disadvantageous in that only selected inks may be used and the coloration characteristic of the magnetic ink is often unacceptable.
Apart from the aforesaid methods, there is also well known the so-called plane ink jet method, which comprises arranging the ink in a slitlike inkholder in parallel to an electrode array, and jetting the ink in accordance with an electric field pattern formed between an electrode facing the electrode array through recording paper. Since no minute orifice for storing ink is required in this method, the problem of ink clogging is minimized. However, high voltage applied for jetting the ink makes it necessary to drive the electrode array on a time division basis to prevent a voltage leak across adjoining or neighboring electrodes. Again, this disadvantage limits the recording speed.
There has also been proposed the so-called heat bubble method for jetting ink out of an orifice by means of thermal energy. In this method, the ink is abruptly heated to cause film boiling. The pressure rise resulting from the rapid formation of bubbles within the orifice is utilized to jet the ink. However, the film boiling temperatures are as high as 500.degree.-600.degree. C. and this makes it difficult to put this method to practical use because the ink properties tend to change with increasing temperature and because a protective layer covering the heating resistor is deteriorated by the high temperatures.
As set forth above, there are many problems remaining to be solved in the ink jet methods heretofore developed. Such problems include difficulty in sufficiently increasing recording speed, the necessity of employing special ink and contriving a particular driving means, and possible thermal deterioration of the ink and the heating means.